Boeing 737-832 N3742C incident near 66 Nm East Of Hobe Sound, Florida

Probable cause

Air traffic controllers did not maintain required awareness of available flight data and aircraft positions, resulting in issuance of an incorrect altitude clearance that caused a loss of standard instrument flight rules separation between the two aircraft.

NTSB analysis

A Boeing 737-800 and an Airbus 319 were transiting Miami Air Route Traffic Control Center (ARTCC) airspace on nearly opposite direction crossing courses when a loss of separation between the two airplanes occurred. The pilots of both airplanes received resolution advisories from the airplanes’ Traffic Alert and Collision Avoidance Systems and took the advised actions to reestablish required separation.

The airplanes were operating in the same Miami ARTCC sector, but were under the control of two different air traffic controllers when the loss of separation occurred. The first controller, who was originally handling the Airbus 319, stated that, although the airplane had not yet left the incident sector, he had transferred responsibility for the airplane to the second controller. After doing so, the first controller dropped the data tag for the Airbus 319 from his radar display and became occupied with other duties. One of those additional duties involved handling the Boeing 737 that had just entered the incident sector, transferred by the controller who was now responsible for handling the Airbus 319. The first controller did not maintain awareness of the Airbus's position, and he did not notice the impending conflict with the Boeing 737 when he subsequently cleared that airplane to climb to the Airbus’ altitude.

The second controller, who transferred control of the Boeing 737 to the first controller, had dropped the data tag for that airplane from his radar display when it left his sector. He was not aware of the conflict between the two airplanes until the radar conflict alert activated. At that time, both controllers attempted to resolve the situation, but a loss of separation occurred. At the closest point, the airplanes were within about 1,800 feet vertically and 2.81 miles laterally of each other. Federal Aviation Administration standards require minimum separation of either 2,000 feet vertically or 5 miles laterally between aircraft operating on instrument flight rules.

Text from the NTSB. Open the NTSB docket for OPS11IA101 for the full record.